Research On Sealing Characteristics Of Metal O-Ring Of Bolted Flange Joint

Sealing performance of spacecraft bolted flange joints could be affected by complex operating conditions such as high temperature and high pressure.At present,few studies on the sealing characteristics of spacecraft flange seals and flange structures are carried on,and most of the existing researches are based on experimental analysis,lacking systematic numerical analysis results.In order to study the sealing characteristics of spacecraft flanges,this thesis firstly conducted compression rebound analysis on the metal O-ring of GH4169 alloy,studying the sealing characteristics of O-ring;Strength verification and sealing performance analysis were conducted on the bolt flange structure,and the stress and deformation characteristics of the flange under high-temperature loads were analyzed.Finally,the flange sealing performance under different influencing factors was evaluated.The main conclusions of this thesis are as follows:(1)An elastic-plastic finite element analysis was conducted on the metal O-ring to study its stress and deformation under different compression.The results showed that as the compression increased,the maximum stress of the Oring existed on the upper and lower surfaces,as well as at the left and right bending points,and the plastic deformation in these areas also increased.The maximum contact stress showed an overall increasing trend.The effects of outer diameter,wall thickness,and surface coating of metal O-rings on their sealing performance were studied.The results showed that under the same compression,the larger the diameter to thickness ratio,the smaller the compression load required.Taking the maximum contact stress and plastic deformation after unloading of the O-ring as the target values,a multi-parameter impact analysis was conducted on the metal O-ring.The results showed that the outer diameter,wall thickness,and compression amount had a significant impact on the maximum contact stress of the O-ring.The outer diameter and compression amount had a significant impact on the maximum plastic strain of the O-ring after unloading,while the wall thickness had a significant impact on the maximum plastic strain of the O-ring after unloading.The selection of O-ring should comprehensively consider the influence of outer diameter,wall thickness,and compression on the rebound and contact stress of the O-ring.(2)The strength of the bolt flange joint was examined under pretightening and operating conditions,and the changes of bolt stress and O-ring contact stress were analyzed.The results indicated that the designed flange structure strength met the requirements.The stress of the bolt increased first and then decreased along the length direction,and the stress on the inner surface was much higher than that on the outer surface.Under pre-tightening conditions,the upper and lower surface of the O-ring were in bilateral contact,and the contact stress distribution was relatively uniform.Under operating conditions,the upper surface of the O-ring was in bilateral contact,while the lower surface was in unilateral contact,and the maximum contact stress did not change much compared to the pre-tightening condition.The steady-state temperature field and high-temperature thermo-solid coupling were conducted on the bolted flange joint.The results showed that the temperature gradient of the flange decreased linearly from the inner surface to the outer surface,and the hightemperature load could lead to an increase in flange stress and axial deformation.The impact of high-temperature loads on the axial displacement of the flange and the distribution of contact stress on the O-ring should be focused in order to avoid high-temperature failure of the flange structure when designing the bolted flange.(3)The effects of O-ring installation position,bolt spacing(quantity),bending moment,internal pressure and temperature fluctuations on flange sealing performance were studied.The results indicated that the contact between the O-ring and the sidewall during installation could cause significant local stress on the sidewall under operating conditions,and the radial contact stress distribution on the upper and lower surfaces could also be affected.An increase in the angle between the bolts could lead to an increase in the difference in contact stress between the inside and outside of the O-ring.When the angle increased to a certain value,the contact state would change to unilateral contact.An increase in axial displacement and rotation angle on the tension side of the flange,and a decrease in axial displacement and rotation angle on the compression side will be caused due to bending moment.The contact stress on the tension side of the O-ring decreased,while the contact stress on the compression side increased.Flange stress would be changed due to internal pressure and temperature fluctuations.The axial displacement and rotation angle decreased with the decrease of internal pressure and temperature.The internal pressure fluctuation had a more significant impact on the flange angle compared to temperature fluctuation.The impact of additional bending moment loads on flange deflection and O-ring contact stress should be focused in order to avoid uneven stress on the flange leading to seal failure.